Genes in mitochondria and chloroplasts code for essential proteins used in respiration and photosynthesis, and for parts of their own protein synthetic machinery. They differ from nuclear genes in having many copies per cell, in the frequency with which they undergo mutation and recombination, in being inherited mainly from the female parent, and in showing rapid loss of heterozygosity. As a result, their evolutionary behavior is very different from nuclear genes, and they offer unique opportunities to investigate some general problems of evolution and population genetics. Understanding organelle gene diversity in populations is important for assessing agricultural crop improvement programs. Long-range objectives of this project are to (i) evaluate organelle gene diversity at the DNA level in plants; (ii) determine mechanisms and rates of organelle DNA evolution in algae; and (iii) develop theory for organelle evolution and population genetics. Specific aims for the project period are: (i) Extend our survey of organelle gene diversity from the chloroplast to the mitochondrial genome of a wild plant. The survey (by restriction analysis) will measure diversity in known genes and noncoding sequences of the mitochondrial DNA from individual plants throughout the range of the species. (ii) Determine the structure of DNA and of specific genes in the plastid of two species of an alga, Polytoma, which has lost its photosynthetic function. Comparisons with plastid genes of photosynthetic relatives will provide information about evolutionary mechanisms and rates with and without selection, and may also allow the identification of a new class of nonphotosynthetic genes. (iii) Extend the existing theory of organelle evolution and population genetics to include the effects of selection, population subdivision, population bottlenecks, and co-evolution of organelle and nuclear genes.